Updated dev requirements for react/http to 0.8.6

Author: christoph-kluge

composer.json

@@ -26,7 +26,7 @@
     },
    "require-dev": {
         "phpunit/phpunit": "^4.8.10||^5.0",
-        "react/http": "^0.8.1",
+        "react/http": "^0.8.6",
         "ringcentral/psr7": "^1.2"
     },
     "scripts": {